Ultrasonic Antifouling

Serendipity
David Caukill
Sat 22 Jun 2013 23:20

Sunday 23rd  June, The Coral Sea, South Pacific Ocean  16:39S  164:27E 

Today’s Blog by David (Time zone BST +10.00; UTC +11.00)

 

 

Anyone who has crossed an ocean will recall the infestation of barnacles – quite possibly 100-200 – which attach to the hull,   particularly under the transom and the top of the rudder,  in the area in which there  are lots of bubbles (oxygen) and also a coral like encrustation that  attaches itself to anywhere it can get a grip.  

 

Here are two photos of Serendipity taken last June in Fiji – less than six months after she was antifouled in St Lucia.

 

 

These were taken after the hull had been washed down with a high pressure hose – the area to the right of the refrigerator keel coolers (for that is what they are!) shows the bottom before wash down because that is where the sling  held the boat - so you can see she gets pretty mucky.  This is a problem for two reasons: it produces drag which slows the boat down – can cost up to a knot which is a bore on long passages – and also some countries approach visiting yachts with long tongs; Australia, for instance, wants evidence of the date of your last antifouling, will visually inspect the waterline and can order an immediate  haul out and wash down in a quarantine area – not the cheapest way of getting things done!

 

To solve the problem, the Fiji guys suggested a soft antifoul – one that gradually  washes off – the idea being that the  encrustation washes off with it.  Well, by the time I got to New Zealand it had  washed off completely - and the growth was back.   (Memo to files: Soft antifouling not ideal for high mileage boats!)

 

Ultrasonic antifouling is not a coating, but essentially a vibrator glued to the inside of the hull (because Serendipity is a larger boat there are two such units). These units make an annoying high pitched screech every 30 seconds or so – a bit like a very, very loud mosquito.  (I say annoying because if I happen to be swimming under the boat for inspection I have to ask for the unit to be switched off). You can’t hear more than a gentle clicking inside the boat but to the passing barnacle, polyp and other coral like encrustations that generally attach to a boat’s hull,  the noise is said to put them off.   Indeed the Australian Navy is said to swear by it.   

 

I investigated it briefly at the London Boat Show.  It is a relatively new idea. The salesmen at LBS were all young and spotty – never owned a boat between them - and  seemed prepared to make wild claims about its efficacy – none of them could produce independent product trial result nor provide evidence for their wild claims.  

 

Well,……. I believed it.  More accurately,  I concluded that the cost of installation would be less than half of the cost of a haul out, wash off and renewed application of the conventional antifouling that it was worth the risk.  So even if it increased the gaps between haul out only by a couple of months it would pay back in 18 months.  I investigated the availability of these systems in NZ and eventually decided to take the plunge. 

 

It is nearly six months since she was hauled out and antifouled (with a conventional hard antifoul)  in New Zealand – and since then we have sailed nearly 2500 miles – so contemplating our passage to Australia we decided we needed to do what we could to clean the bottom.  It was with some trepidation then that we dived in for inspection.

 

Truthfully, the results have been quite staggering!   There was not one barnacle on the surface of the hull. Although there were a couple in the through hull fittings they came off easily and there was no coral like encrustation – at all.  There was a light coating of what seemed to be an algae but that wiped off with a cloth. Working together we were able to clean the whole hull, and restore it to her newly antifouled condition in less than two hours.  

 

Quite astonishing really – I doubt we will need to haul out until South Africa now – next Christmas.

 

RESULT!